Reland "[iOS][Alert] Add alert controller to Showcase"

This reverts commit 7eacffe7807333a6a2407aeb7f13a4734fec3cdf.

Reason for revert: Underlying issue has been fix.

Original change's description:
> Revert "[iOS][Alert] Add alert controller to Showcase"
> 
> This reverts commit 2410dcb91e53dec59d02a983a5a4c186bc1d854d.
> 
> Reason for revert: Bug 954134
> 
> Original change's description:
> > [iOS][Alert] Add alert controller to Showcase
> > 
> > Bug: 951301, 951300
> > Change-Id: If0af93103f0038ad35770cee09b94b455aeca92b
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1561109
> > Commit-Queue: Javier Ernesto Flores Robles <javierrobles@chromium.org>
> > Reviewed-by: edchin <edchin@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#652122}
> 
> TBR=edchin@chromium.org,javierrobles@chromium.org
> 
> Bug: 954134
> Change-Id: I4f4d441cf3fa9ea5651a0b0bc01ef41e9bd0f277
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: 951301, 951300
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1573639
> Reviewed-by: François Doray <fdoray@chromium.org>
> Commit-Queue: François Doray <fdoray@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#652127}

TBR=fdoray@chromium.org,edchin@chromium.org,javierrobles@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 954134, 951301, 951300
Change-Id: I1740cd09d71efea1f982b8617eb4b7c940efa26e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1574720
Reviewed-by: Javier Ernesto Flores Robles <javierrobles@chromium.org>
Commit-Queue: Javier Ernesto Flores Robles <javierrobles@chromium.org>
Cr-Commit-Position: refs/heads/master@{#652539}
5 files changed